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Yu Wang,Zhihui Li,Baiqing Xiong,Kai Wen,Shuhui Huang,Xiwu Li,Yongan Zhang 대한금속·재료학회 2019 METALS AND MATERIALS International Vol.25 No.3
Microstructure evolution of a new high-alloyed Al–Zn–Mg–Cu–Zr–Sc aluminium alloy during two-stage homogenizationprocess was investigated by use of scanning electron microscope, transition electron microscope and high resolution transitionelectron microscope. The results indicate that the morphology and chemical composition of Al 3 (Sc, Zr) particles formedin the fi rst stage were greatly aff ected by heating temperature. With the increase of heating temperature, the morphologyof Al 3 (Sc, Zr) particles transform from cuboidal with evident faceting to spheroidal due to improved Zr diff usivity. MoreZr atoms enrich in the interface of precipitate/matrix forming a thin layer. Moreover, the mean diameter of precipitatesincreases a little bit with the increase of heating temperature, showing very restricted coarsening rate and high thermal stabilityof Al 3 (Sc, Zr) particles. After an appropriate second stage heat treatment (474 °C × 48 h), the intermetallic formed inthe solidifi cation process could dissolve suffi ciently and Al 3 (Sc, Zr) particles still keep very good coherency with Al matrixwithout abnormal growth.
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Kai Wen,Baiqing Xiong,Yongan Zhang,Zhihui Li,Xiwu Li,Lizhen Yan,Hongwei Yan,Hongwei Liu 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.5
Precipitation characteristics influencing fatigue crack propagation contained matrix precipitate, grain boundary precipitateand precipitate free zone for Al–Zn–Mg–Cu alloys. Over-aging treatment could effectively regulate precipitation and then tobe able to change fatigue crack propagation behavior compared with the peak aging state. In the current work, typical T651and T7651 aging tempers of the alloy were extracted via hardness, electrical conductivity and mechanical properties underone-step and two-step aging treatments. Fatigue crack propagation (FCP) rate under them was tested and correspondingprecipitation characteristics and fracture morphology were observed. The results indicated that fatigue crack propagationresistance for the T7651 temper possessed an obvious improvement on the side of that for the T651 temper, which was alsosupported by fracture appearance, including tearing ridge, tearing dimple and fatigue striation. The precipitation observationshowed that the T651 alloy contained GPI zone, GPII zone and ηʹ phase while the T7651 alloy possessed ηʹ phase and η phase.Compared with the T651 temper, matrix precipitate for the T7651 temper distinctly owed an expanding of size distributionand an enlargement of average size while cuttable phase still remained the dominance for both tempers. Grain boundaryprecipitate and precipitate free zone manifested no obvious difference between the two aging tempers. Cut and bypass mechanismsof dislocation–precipitate interactions were used for explanation and it revealed the reinforced cuttable phase was infavor of enhancing fatigue crack propagation resistance. A theoretical model which directly correlated FCP rate with matrixprecipitate characteristics was employed to calculate FCP rate by substituting quantitative precipitate characteristics and thecalculation results were vaguely consistent with the experimental measurement, which proved its reliability and feasibility.
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Kai Wen,Baiqing Xiong,Yongan Zhang,Zhihui Li,Xiwu Li,Shuhui Huang,Lizhen Yan,Hongwei Yan,Hongwei Liu 대한금속·재료학회 2018 METALS AND MATERIALS International Vol.24 No.3
In the present work, the infl uence of various retrogression treatments on hardness, electrical conductivity and mechanicalproperties of a high Zn-containing Al–Zn–Mg–Cu alloy is investigated and several retrogression regimes subjected to a samestrength level are proposed. The precipitates are qualitatively investigated by means of transmission electron microscopy(TEM) and high-resolution transmission electron microscopy techniques. Based on the matrix precipitate observations, thedistributions of precipitate size and nearest inter-precipitate distance are extracted from bright-fi eld TEM images projectedalong ⟨110⟩ Al orientation with the aid of an imaging analysis and an arithmetic method. The results show that GP zonesand η′ precipitates are the major precipitates and the precipitate size and its distribution range continuously enlarge with theretrogression regime expands to an extent of high temperature. The nearest inter-precipitate distance ranges obtained arequite the same and the average distance of nearest inter-precipitates show a slight increase. The infl uence of precipitates onmechanical properties is discussed through the interaction relationship between precipitates and dislocations.
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Jingtian Wang,Lei Fang,Qidi Wu,Dongdong Li,Zhongming Huo,Xiwu Yan 한국유전학회 2020 Genes & Genomics Vol.42 No.1
Introduction AMP-activated protein kinases (AMPK) are heterotrimeric complexes. The main upstream phosphorylase has AMP-dependent LKB1 and Ca2+-dependent CaMKK beta. AMPK also includes an auto-inhibitory domain and a region associated with beta and gamma subunits, which regulate a variety of cellular activities and energy metabolism. The increase in the ratio of AMP/ATP can stimulate the activation of AMPK. Once AMPK is activated, pathways to ATP consumption (e.g., fat, cholesterol, and protein synthesis) will be shut down. The pathway to ATP generation (e.g., oxidation of fat and glycolysis pathway) will be activated. AMPK genes have not been systematically characterized in marine invertebrates. Methods In this study, we identified and characterized three AMPK genes, AMPK-α, AMPK-β, and AMPK-γ, in the Manila clam (Ruditapes philippinarum). To gain insight into the role of AMPK genes during clam energy metabolism, quantitative real-time PCR was used to investigate the expression profiles in the different stages of clam development, in healthy adult tissues, and after air exposure at two different temperatures. Results Phylogenetic and protein structural analyses were conducted to determine the identity and evolutionary relationships of these genes. The structural features of the genes were relatively well-conserved, relative to the AMPK genes of other vertebrates. The expression of genes was significantly induced 3–48 h after air exposure. Conclusinon AMPK-α, AMPK-β and AMPK-γ are involved in clam energy metabolism. Increased expression levels of AMPK genes in the gill and intestine of Manila clam in response to air exposure implied a strong adaptability to the coastal environment.
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